Bit holder device

ABSTRACT

Provided is a bit holder device which is capable of driving a screw into a workpiece, while holding the screw having a groove in which a bit body is inserted, and which makes it possible to change the bit body without removing it from a chuck of an electric tool, etc. A bit holder device facilitating the attachment and detachment of a cylindrical body is also provided. A bit holder device for driving a screw, while holding the screw against detachment from a bit body with retaining a state where an end of the bit body is inserted in a groove on a head of the screw, has a cylindrical cover member removably fitted about the bit body from the end of the bit body, the cover member has an end including a magnetic attracting portion for magnetically attracting the head of the screw, and the bit body protrudes from the end of the cover member.

TECHNICAL FIELD

This invention relates to a bit holder device which enables a job oftightening or the like of a screw, etc., while holding the screw againstdetachment from a bit body with retaining a state where the bit body isengaged with the groove on the head of the screw, etc.

BACKGROUND ART

A conventional bit holder device which holds a screw, etc. withretaining a bit body inserted in the groove on the head of the screw,etc. to facilitate a job of tightening, driving into a workpiece, or thelike of the screw is disclosed in, for example, JP-A-2000-246658.

What is disclosed in that publication consists of a cylindrical bodyfitted on a bit body attached to an electric tool, and the cylindricalbody is provided with holding means (a magnet) for holding a screw withthe bit body inserted in the groove of its head.

The use of the cylindrical body has, however, makes the attachment anddetachment of the bit and cylindrical bodies cumbersome, since two jobs,that is, the job of removing the bit body from the chuck of the electrictool and the job of removing the cylindrical body from the bit body arerequired for changing the bit body and attaching the cylindrical body toanother bit body.

A bit holder device as disclosed in German Patent PublicationDE10148943A1 is known as a type in which the bit body is removably heldby a holder body having a shank in its rear portion. The devicedescribed in the German Patent Publication has, however, a drawback thatthe cylindrical body cannot be removed from the holder body.

-   Patent Literature 1: JP-A-2000-246658-   Patent Literature 2: German Patent Publication DE10148943A1

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In view of these circumstances, it is an object of this invention toprovide a bit holder device which is capable of driving a screw into aworkpiece, while holding the screw with a groove thereof engaged with abit body so as not to be detached from the bit body, and which makes itpossible to change the bit body easily without removing the bit bodyfrom a chuck of an electric tool, etc.

It is another object of this invention to provide a bit holder devicewhich facilitates the attachment and removal of a cylindrical body.

Means for Solving the Problems

In order to attain the above objects, this invention provides technicalmeans as described below.

A bit holder device for driving a screw, while holding it againstdetachment from a bit body with retaining a state where an end of thebit body is inserted in a groove on a head of the screw, has acylindrical cover member removably fitted about the bit body from theend of the bit body, the cover member has an end including a magneticattracting portion for attracting the head of the screw magnetically,and the bit body protrudes from the end of the cover member.

This facilitates a job of changing the bit body, since the cover memberis removable and the job of changing the bit body can be performed afterthe cover member is removed. The screw can be held by the magneticattracting portion provided on the cover member fitted about a holderbody.

The bit body is removably held by the holder body having a shank in itsrear portion, and the cover member is fitted about the holder body.

This simplifies the job of changing the bit body, since the bit body canbe changed while the shank remains attached to an electric tool, etc.

Movement permitting means is provided between an inner surface of thecylindrical cover member and an outer surface of the holder body forpermitting an axial back and forth movement of the cover member relativeto the holder body.

With this arrangement, since the back and forth movement of the covermember is permitted by the movement permitting means, the cover membercan be retracted when no screw is thereby held, so that the bit body canprotrude to a greater extent to facilitate the insertion of a screw intothe bit body. Moreover, the magnetic force exerted by the magneticattracting portion on the screw upon its insertion into the bit bodycauses the cover member to advance and hold the screw on its magneticattracting portion.

The Movement permitting means consists of a circumferential grooveformed in the outer surface of the cylindrical holder body and anelastic annular member provided on the inner surface of the cover memberto be engaged with the circumferential groove, and the circumferentialgroove has an axial length which is greater than that of the elasticannular member.

This permits the cover member having the elastic annular member to moveback and forth to the extent defined by the axial length of thecircumferential groove. Accordingly, the distance by which the covermember is permitted to move back and forth can be set by setting theaxial length of the circumferential groove.

The holder body is formed in a cylindrical shape and has a portionforward of its circumferential groove having a diameter which is equalto, or slightly smaller than the inside diameter of the elastic annularmember.

This enables the elastic annular member to be fitted easily in thecircumferential groove of the holder body.

The magnetic attracting portion is an annular magnet provided at a frontend of the cover member and the bit body has a tapered tip portion sosituated as to cross the front end face of the magnet.

This enables the tapered portion of the bit body to be magnetized by theannular magnet so that the bit body and the magnet may cooperate to holdthe screw more securely and thereby tighten it, etc. in a more stableposition.

The bit body has a shank integrally formed with its rear portion, andthe cover member is directly fitted about the bit body.

With this arrangement, since the cover member is removably fitted aboutthe bit body, the cover member can be easily removed.

The cover member is held by retaining means for preventing detachment ofthe bit body, and the retaining means is formed of an elastic materialto allow the attachment and detachment of the cover member by a humanforce.

The retaining means formed of an elastic material enables the covermember to be attached or detached easily only by manually pulling thecover member with a force causing the elastic deformation of the elasticmaterial.

The holder body has a raised portion formed at its rear end forpositioning the cover member fitted about the holder body.

This enables the cover member to be situated in the same position at anytime when the bit holder device does not hold any screw.

The bit body is removably held by the holder body having a shank in itsrear portion, the cover member is removably fitted about the holderbody, movement permitting means is provided between the inner surface ofthe cylindrical cover member and the outer surface of the holder bodyfor permitting the axial back and forth movement of the cover memberrelative to the holder body, the movement permitting means consists of acircumferential groove formed in the outer surface of the cylindricalholder body and an elastic annular member provided on the inner surfaceof the cover member to be engaged with the circumferential groove, thecircumferential groove has an axial length which is greater than that ofthe elastic annular member, and the elastic annular member defines theretaining means.

With this arrangement, since a screw can be held by the magneticattracting portion provided on the cover member fitted about the holderbody, and since the back and forth movement of the cover member ispermitted by the movement permitting means, the cover member can beretracted when no screw is thereby held, so that the bit body canprotrude to a greater extent to facilitate the insertion of a screw intothe bit body. Moreover, the magnetic force exerted by the magneticattracting portion on the screw upon its insertion into the bit bodycauses the cover member to advance and hold the screw on its magneticattracting portion.

Further, since the elastic annular member fitted in the circumferentialgroove is employed for restricting the back and forth movement of thecover member, the cover member can be detached from the holder body onlyby pulling it with a force causing the elastic deformation of theelastic annular member. The cover member can be fitted about the holderbody easily only by elastically deforming the elastic annular member toforce it into the circumferential groove. Moreover, the attachment anddetachment of the cover member to and from the holder body can be easilydone by a single hand. Accordingly, since the bit body can be changed bythe detachment of the cover member by a single hand, any job of changingof the bit body can be done easily and quickly.

The bit body has a shank integrally formed with its rear portion, thecover member is fitted directly about the bit body, and there isprovided movement permitting means between the inner surface of thecylindrical cover member and the outer surface of the bit body forpermitting the axial back and forth movement of the cover memberrelative to the bit body. The movement permitting means consists of acircumferential groove formed in the outer surface of the bit body andan elastic annular member provided on the inner surface of the covermember to be engaged with the circumferential groove. Thecircumferential groove has an axial length which is greater than that ofthe elastic annular member, and the elastic annular member serves as theretaining means.

With this arrangement, when the bit body protruding from the front endof the cover member is inserted in the groove of the head of a screw,since the head of the screw is magnetically attracted to the magneticattracting portion of the cover member, the screw can be held againstseparation from the bit body when it is attached to a workpiece, therebyfacilitating any job of tightening, driving, or the like of a screw,etc.

When the bit body is securely inserted in the groove of a screw, etc,the cover member is moved toward the screw by the movement permittingmeans, enabling the magnetic attracting portion of the cover member tohold the screw.

Thus, the bit holder device can always hold any screw with the tip ofits bit body fit completely in the head of the screw.

The elastic annular member engaged with the circumferential grooveserves as a retainer, and the cover member having the elastic annularmember is permitted to move back and forth to the extent defined by theaxial length of the circumferential groove. Accordingly, the distance bywhich the cover member is permitted to move back and forth can be set bysetting the axial length of the circumferential groove.

Moreover, the bit body can be changed only by detaching the cover memberfrom the holder body. Accordingly, it is possible to save the trouble toloosen the chuck, etc. of an electric tool for changing the bit.

Advantages of the Invention

According to this invention, it is possible to drive a screw into aworkpiece, while holding the screw with a groove thereof engaged with abit body, and to change the bit body easily without loosening a chuck ofan electric tool, etc. for removing the bit body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing a bit holder deviceaccording to this invention when it holds a screw.

FIG. 2 is a longitudinal sectional view showing the bit holder devicewhen it has driven the screw into a workpiece.

FIG. 3 is an exploded view of the bit holder device.

FIG. 4 includes a set of side elevational views showing a process inwhich a cover member is fitted on a holder body.

FIG. 5 is a side elevational view of the bit holder device.

FIG. 6 is a side elevational view explaining the action in which thescrew is magnetically attracted by the magnetic attracting portion ofthe cover member.

FIG. 7 is a longitudinal sectional view showing a bit holder device whenit does not hold any screw.

FIG. 8 is a longitudinal sectional view showing the bit holder devicewhen it holds a screw.

FIG. 9 is a longitudinal sectional view showing a bit holder device whenit does not hold any screw.

FIG. 10 is a longitudinal sectional view showing the bit holder devicewhen it holds a screw.

FIG. 11 is a longitudinal sectional view showing a bit holder devicewhen it does not hold any screw.

FIG. 12 is a longitudinal sectional view showing the bit holder devicewhen it holds a screw.

FIG. 13 is a longitudinal sectional view showing a bit holder devicewhen it does not hold any screw.

FIG. 14 is a longitudinal sectional view showing the bit holder devicewhen it holds a screw.

BEST MODE OF CARRYING OUT THE INVENTION

The best mode of this invention will now be described with reference tothe drawings.

The bit holder device (screw catch bit holder device) 1 of thisinvention enables a job of tightening, driving, or the like of a screw3, while holding the screw 3 against detachment from a bit body 2rotatably attached to an electric rotating tool B, such as an electricscrewdriver, and engaged with a groove on a head of the screw 3.

FIGS. 1 to 6 show a first embodiment of this invention.

The bit holder device 1 has a holder body 4 removably holding the bitbody 2, and a cover member 5 to be attached to the holder body 4. Theholder body 4 removably holds the bit body 2 in its front portion andhas a shank 6 in its rear portion. The holder body 4 is made of a metal,and according to the embodiment under description, it is formed ofstainless steel (for example, SUS304). The shank 6 is formed in theshape of a hexagonal column so as to be attached to the electricrotating tool B.

The holder body 4 is cylindrical (for example, circular cylindrical) andhas a first holding port 7 for holding the bit body 2 at onelongitudinal end thereof (hereinafter referred to as its front end). Asecond holding port 8 for holding the shank 6 is formed at the other endof the holder body 4 (hereinafter referred to as its rear end). Thedirection extending through the cylindrical (or axial) center of theholder body 4 is referred to as its longitudinal direction.

The first holding port 7 is formed with a regular hexagonal edge and thetrunk portion of the bit body 2 having a hexagonal column shape isfitted therein. Holding means 9 for removably holding the bit body 2 isprovided on the inner surface of the first holding port 7.

The holding means 9 has a groove 10 formed in the inner wall of thefirst holding port 7 about its axial center, and a stopper ring 11fitted in the groove 10. The bit body 2 has a notch 12 formed at eachcorner of its shank portion, such that the stopper ring 11 is engagedwith the notches 12 of the bit body 2 to retain the bit body 2 inposition when the bit body 2 is fitted in the first holding port 7 andheld by the holder body 4, as shown in FIGS. 1 to 3. The bit body 2 canbe removed from the first holding port 7 by pulling out it only with aforce causing the stopper ring 11 to be elastically deformed anddisengaged from the notches 12.

The shank 6 has a circumferential groove 6a formed at one longitudinalend of its trunk portion (or its rear end), which serves as anattachment portion to the electric rotating tool B. The shank 6 has ahead 6b formed at its front end and contacting the bottom of the secondholding port 8. The head has a front end surface formed in a circularshape and at its front end, the head 6 b has a diameter which isslightly smaller than the diameter of the inscribed circle of theregular hexagon of the trunk portion of the shank 6 in the shape of ahexagonal column.

The second holding port 8 is formed with a circular edge in the rear endsurface of the holder body 4. The second holding port 8 has a diameterwhich is substantially equal to, or slightly larger than that of thehead at its front end, and slightly smaller than that of thecircumscribed circle of the regular hexagon of the shank 6 in the shapeof a hexagonal column.

The holder body 4 has a circumferential groove 13 formed in the outersurface of its axially (or longitudinally) middle portion. Thecircumferential groove 13 is formed along the outer periphery of thecylindrical holder body 4. The circumferential groove 13 has a wallsurface (hereinafter referred to as a rear wall surface 15), on thecloser side to the second holding port 8, which is formed as a tapered(or inclined) surface reduced in diameter (or tapered) toward its frontend (in the direction from the second holding port 8 to the firstholding port 7).

The circumferential groove 13 also has a wall surface (hereinafterreferred to as a front wall surface 16), on the closer side to the firstholding port 7, which is formed as a tapered (or inclined) surfaceenlarged in diameter toward its front end (in the direction from thesecond holding port 8 to the first holding port 7). A straight portion14 in a column shape is formed between the rear and front wall surfaces15 and 16.

The holder body 4 has an annular raised portion 17 formed on its outersurface between the front wall surface 16 and the first holding port 7.The annular raised portion 17 has a wall surface 17 a, on the closerside to the first holding port 7 (or on its front side), which is formedas a tapered (or inclined) surface reduced in diameter in the directionfrom the second holding port 8 to the first holding port 7.

The holder body 4 has in its trunk portion forward of itscircumferential groove 13, or more specifically forward of its annularraised portion 17, a diameter which is equal to, or slightly smallerthan the inside diameter of an elastic annular member 24 which will bedescribed later.

The cover member 5 is cylindrically shaped so as to be removably fittedabout the holder body 4. The cover member 5 has a port 18 formed at onelongitudinal end thereof (hereinafter referred to as its rear end) forthe insertion of the holder body 4 therethrough. The other end of thecover member 5 (hereinafter referred to as its front end) includes amagnetic attracting portion 19 for holding the screw 3. The magneticattracting portion 19 has an annular magnet 20 and is fitted inside thefront end of the cover member 5. The annular magnet 20 has a holethrough which the bit body 2 extends and projects forward through thefront end.

The cover member 5 has a radially inwardly projecting wall portion 21formed on the inner surface of its axially intermediate portion andalong its inner circumference. The wall portion 21 has a hole formed forthe insertion of the bit body 2 therethrough. The wall portion 21 isformed to enable a concavity 22 in which the magnet 20 is fitted to beformed at the other end of the cover member 5. The wall portion 21 has asurface facing the other end of the cover member 5 and defining thebottom of the concavity 22.

The cover member 5 has a circumferential groove 23 formed along itsinner circumference in the inner surface of its axially intermediateportion. The circumferential groove 23 is formed rearward of the wallportion 21. An annular body formed of an elastic material (hereinafterreferred to as an elastic annular member 24) is fitted in thecircumferential groove 23. An O-ring is, for example, used as theelastic annular member 24, which has a circular cross section and isdisposed to project inwardly from the inner surface of the cover member5.

The elastic annular member 24 is engaged with the circumferential groove13 of the holder body 4 when the cover member 5 is put on the holderbody 4, as shown in FIG. 1.

Specifically, under a state where the cover member 5 is put on theholder body 4, the elastic annular member 24 stays between the rear andfront wall surfaces 15 and 16 of the circumferential groove 13 and ismovable back and forth. The elastic annular member 24 has an insidediameter larger than the diameter of the straight portion 14 of thecircumferential groove 13 of the holder body 4 and the elastic annularmember 24 staying in the circumferential groove 13 is movable back andforth without contacting the straight portion 14.

The inside diameter of the elastic annular member 24 is smaller than theoutside diameter of the annular raised portion 17 on the outer surfaceof the holder body 4, so that when the cover member 5 has moved to aforwardmost position, the elastic annular member 24 abuts the sidesurface of the annular raised portion 17 (or the front wall surface 16of the circumferential groove 13) to prevent the detachment of the covermember 5 from the holder body 4. Thus, the elastic annular member 24serves as retaining means for the cover member 5.

The cover member 5 radially outwardly bulges in an axially intermediateportion of its outer surface. This bulging portion 25 is formed to becaught by fingers pinching the cover member 5 so as to facilitate theapplication of a force for attaching the cover member 5 onto the holderbody 4. The cover member 5 also has an elastic annular member 27 fittedon the outer surface of substantially its axially middle portion. Theelastic annular member 27 is fitted in a circumferential groove formedadjacent to the bulging portion 25. An O-ring is, for example, used asthe elastic annular member 27 and it serves as a slip stopper when thecover member 5 is detached from the holder body 4.

The cover member 5 has ridges and grooves formed on its outer surfacebetween the elastic annular member 27 and the insertion port 18 andserving as a slip stopper when the cover member 5 is pinched.

The cover member 5 is fitted on the holder body 4 in a way as describedbelow.

The insertion port 18 at one longitudinal end of the cover member 5 isplaced about the front end of the bit body 2 attached to the holder body4. Then, the cover member 5 is forced along the holder body, so that thefront end of the holder body 4 is passed through the elastic annularmember 24 in the cover member 5.

When the cover member 5 is further forced along, the elastic annularmember 24 abuts the wall surface 17 a on the first holding port 7 sideof the annular raised portion 17 formed on the outer surface of theholder body 4, as shown in FIG. 4(a). This wall surface will hereinafterbe referred to as the abutting inclined surface 17 a. When the covermember 5 is further forced along strongly, the elastic annular member 24abutting the annular raised portion 17 is forced by the annular raisedportion 17 to be elastically deformed with its inside diameter enlarged,as shown in FIG. 4(b).

When the cover member 5 is further forced along and the elastic annularmember 24 has passed the annular raised portion 17, the elasticallydeformed elastic annular member 24 recovers its original shape by itsrestoring force and thereby engages with the circumferential groove 13of the holder body 4, as shown in FIG. 4(c).

The axial length h1 of the circumferential groove 13 is larger (orlonger) than the axial length of the elastic annular member 24 (i.e. thediameter of its circular cross section) h2 (see FIG. 4(a)). Accordingly,the elastic annular member 24 engaged with the circumferential groove 13is allowed to move back and forth by a distance equal to the axiallength of the circumferential groove 13. The circumferential groove 13has a depth so selected that the elastic annular member 24 engaged withthe circumferential groove 13 does not contact the surface of thestraight portion 14.

The magnet 20 attracts with its magnetic force the bit body 2 of amagnetic material so that the front end of the bit body 2 protrudes fromthe cover member 5 through its front end opening. Accordingly, the frontend of the bit body 2 protrudes forward from the front end surface ofthe magnet 20 when the elastic annular member 24 is engaged with thecircumferential groove 13. Moreover, the front end surface of the holderbody 4 abuts the rear end surface of the wall portion 21 of the covermember 5.

Since the magnetic force of the magnet 20 acts on the bit body 2 so thatit protrudes forward through the front end of the cover member 5, astate of contact is maintained between the front end surface of theholder body 4 and the rear end surface of the wall portion 21 of thecover member 5.

The cover member 5 is fitted on the holder body 4 as described above,and since the abutting inclined surface 17 a is a tapered (or inclined)surface reduced in diameter from the second holding port 8 to the firstholding port 7, the elastic annular member 24 is gradually elasticallydeformed by the abutting inclined surface 17 a when it has abutted onthe abutting inclined surface 17 a and is going to engage in thecircumferential groove 13 as described above. Accordingly, since theelastic annular member 24 is neither too quickly deformed nor damaged bythe top of the raised portion 17, the elastic annular member 24advantageously has a prolonged life.

When the cover member 5 is pulled for its detachment from the holderbody 4, the elastic annular member 24 abuts the front wall surface 16 ofthe circumferential groove 13. Accordingly, the elastic annular member24 is gradually elastically deformed by the front wall surface 16, as inits elastic deformation by the abutting inclined surface 17 a.

Since the trunk portion of the holder body 4 forward of itscircumferential groove 13 has a diameter which is equal to, or slightlysmaller than the inside diameter of the elastic annular member 24, themere insertion of the front end of the holder body 4 through the elasticannular member 24 as described above hardly causes any elasticdeformation of the elastic annular member 24.

Accordingly, no excessive frictional force acts between the elasticannular member 24 and the holder body 4, while the cover member 5 ismoved until the elastic annular member 24 through which the front end ofthe holder body 4 is inserted abuts the abutting inclined surface 17 aas described above. Therefore, since the cover member 5 can be movedwithout receiving any resistance until the elastic annular member 24abuts the abutting inclined surface 17 a, the cover member 5 can befitted on the holder body 4 easily.

When the bit body 2 is inserted in the groove on the head of the screw 3as shown in FIG. 6, the magnetic force of the magnet 20 acts on the headof the screw 3 to attract the screw 3. However, as the bit body 2 isinserted in the groove on the head of the screw 3, the head of the screw3 is kept apart from the magnet 20 and is not movable toward the magnet20.

However, since the cover member 5 is movable back and forth by thespecific distance stated before, the magnetic force exerted on the screw3 by the magnet 20 causes the cover member 5 to move toward the screw 3,and the front end surface of the cover member 5, or the front endsurface of the magnet 20 magnetically contacts the surface of the headof the screw 3. As a result, the head of the screw 3 is securely held bythe magnet 20 serving as the magnetic attracting portion 19, so that anyscrew 3 can be held in a stable position whenever it is driven into aworkpiece A.

The cover member 5 is movable relative to the holder body 4 by thedistance between the front and rear edges of the circumferential groove13, since the elastic annular member 24 in the cover member 5 is allowedto move back and forth by the distance between the front and rear edgesof the circumferential groove 13 when engaged with the circumferentialgroove 13 as stated above. Accordingly, this arrangement constitutemovement permitting means 26 provided between the inner surface of thecover member 5 and the outer surface of the holder body 4 for permittingthe axial back and forth movement of the cover member 5 relative to theholder body 4.

That is, the movement permitting means 26 includes the circumferentialgroove 13 formed in the outer surface of the cylindrical holder body 4;and the elastic annular member 24 provided on the inner surface of thecover member 5, engageable in the circumferential groove 13, and movableback and forth.

The front inclined portion of the bit body 2 is arranged to move backand forth across the front end surface of the magnet 20 in the covermember 5 when the cover member 5 moves. This is due to the fact thatwhen the front end surface of the magnet 20 is positioned across theinclined portion of the bit body 2, the bit body 2 is magnetized by themagnet 20 and the bit body 2 itself becomes capable of holding the screw3. Accordingly, the movement permitting means 26 serves also asrestricting means for restricting the front end surface of the covermember 5 for movement in correspondence with the inclined portion of thebit body 2.

When the bit holder device 1 is used to drive the screw 3 into theworkpiece A, such as wood, there are some cases in which the head of thescrew is sunk below the surface of the workpiece A, as shown in FIG. 1.When the head of the screw 3 is sunk below the surface of the workpieceA, the front end surface of the cover member 5, or the outer end surfaceof the magnet 20 contacts the surface of the workpiece A, whereby thescrew 3 and the magnet 20 are released from magnetic contacttherebetween and the cover member 5 retracts relative to the holder body4.

When the front end surface of the cover member 5 is in contact with thesurface of the workpiece A, the front end surface of the holder body 4is in contact with the rear end surface of the wall portion 21 of thecover member 5. These contacts make it possible to prevent any furtherextension of the bit body 2 attached to the holder body 4 and therebyany undesirable sinking of the screw 3 in the workpiece A.

Thus, the contact of the front end surface of the holder body 4 with thewall portion 21 of the cover member 5 restricts the movement of the bitbody 2 so that the screw 3 may not sink in the workpiece A to anygreater extent than is required.

Accordingly, the bit holder device 1 is provided with restricting meansfor restricting the movement of the bit body 2 to prevent sinking of thescrew 3 in the workpiece A to any greater extent than is required, whileallowing sinking of the screw 3 to a specific extent.

It is sufficient to detach the cover member 5 from the holder body 4when changing the bit body 2 in the bit holder device 1 as describedabove, and it is possible to change the bit body 2 easily withoutloosening the chuck of an electric tool B, or the like and removing theholder body 4.

When changing the bit body 2, it is possible to change the bit body 2only by removing the cover member 5. Accordingly, it is possible toeliminate the trouble to loosen the chuck of the electric tool B anddetach the bit body 2, and it is advantageously possible to change thebit body 2 easily without having any annoyance.

FIGS. 7 and 8 show a second embodiment of this invention.

According to the second embodiment of the invention, a holder body 4 hasa radially outwardly extending raised portion 31 formed at its rear end,which is a difference from the first embodiment. The raised portion 31is formed along the whole circumference of the holder body 4 and in anannular shape.

When the bit holder device 1 does not hold any screw 3, the cover member5 is in its standby position in which it is retracted relative to theholder body 4, and is positioned by its rear end 5 a abutting the raisedportion 31 of the holder body 4, as shown in FIG. 7. In this state, thefront end of the holder body 4 is kept apart from the wall portion 21 ofthe cover member 5, and the raised portion 31 solely serves to positionthe cover member 5.

The raised portion 31 does not necessarily need to be annular, as longas it projects outwardly (radially outwardly) from the outer surface ofthe holder body 4 so that the rear end 5 a of the cover member 5 abut itfor positioning.

When a screw 3 is inserted in the bit body 2 shown in FIG. 7, themagnetic force exerted on the screw 3 by the magnetic attracting portion19 of the cover member 5 causes the cover member 5 to advance, so thatits magnetic attracting portion 19 holds the screw 3, as shown in FIG.8.

According to the second embodiment, therefore, the raised portion 31formed at the rear end of the holder body 4 enables the cover member 5to be positioned in the same location at any time in its standbyposition without any screw 3 held, and as in the case of the firstembodiment, the cover member 5 can be detached easily with a single handand can be attached to the holder body 4 easily with a single hand againafter the bit body 2 is changed, so that any job of changing the bitbody 2 can be performed easily.

Other construction of this embodiment is equal to that of the firstembodiment, and common symbols with the first embodiment are used todenote common parts (as will be the case with a third embodiment of theinvention, too).

As an alternative in construction, the bit body 2 may be formedintegrally with the shank 6 and formed with the circumferential groove13 thereon to fit the cover member 5 on the bit body 2 removably withoutemploying any holder body 4. In this case, too, the elastic annularmember 24 and the circumferential groove 13 facilitate the attachmentand detachment of the cover member 5 to and from the bit body 2.

FIGS. 9 and 10 show a third embodiment of this invention.

According to the third embodiment, an elastic annular member 24 providedon the inner side of a cover member 5 and a circumferential groove 13formed on a holder body 4 limit (or restrict) the movement of the covermember 5. When the bit holder device 1 does not hold any screw 3, thecover member 5 is in its standby position in which it is retractedrelative to the holder body 4, as shown in FIG. 9. In this position, theelastic annular member 24 on the inner side of the cover member 5 abutsthe rear wall surface 15 of the circumferential groove 13 and the covermember 5 is so positioned as not to retract any more.

In this position, the holder body 4 has its front end stay away from thewall portion 21 of the holder body 4, and the positioning of the covermember 5 is effected solely by the contact of the elastic annular member24 with the rear wall surface 15 of the circumferential groove 13.

When a screw 3 is inserted in the bit body 2 in this position, the covermember 5 advances and its magnetic attracting portion 19 holds the screw3, as shown in FIG. 10.

The elastic annular member 24, which is situated between the rear andfront wall surfaces 15 and 16 of the circumferential groove 13, allowsthe back and forth movement of the cover member 5 and serves asretaining means for retaining the cover member 5, while positioning itas described. In other words, the circumferential groove 13 and theelastic annular member 24 serve not only as the movement permittingmeans as stated before, but also as positioning means for positioningthe cover member 5 in its standby position in which it is retracted, oras retaining means for preventing the cover member 5 from coming off.

As an alternative in construction, the bit body 2 may be formedintegrally with the shank 6 and formed with the circumferential groove13 thereon to fit the cover member 5 on the bit body 2 removably withoutemploying any holder body 4. In this case, too, the elastic annularmember 24 and the circumferential groove 13 facilitate the attachmentand detachment of the cover member 5 to and from the bit body 2.

FIGS. 11 and 12 show a fourth embodiment of this invention.

According to the fourth embodiment, a bit holder device 1 has a holderbody 4, a bit body 2, and a cover member 5 fitted directly on the bitbody 2 removably and holding a screw 3 by a magnetic force. The holderbody 4 is equal to what is used according to the first to thirdembodiments.

The bit body 2 shown is of the so-called TORX type and has anirregularly shaped end which is engageable in the groove formed in thehead of the screw 3. The bit body 2 has a rear portion 2 a formed in theshape of a hexagonal column as according to the first to thirdembodiments. Its hexagonal column portion has notches 12 formed asdescribed in connection with the first embodiment.

The bit body 2 has a front portion 2 b shaped like a circular column andsmaller in diameter than the rear portion 2 a in the shape of ahexagonal column. The front portion 2 b of the bit body 2 smaller indiameter than the rear portion 2 a serves as a torsion portion which canabsorb any excessive load bearing on the bit body 2 during work andthereby prolong the life of the bit body 2.

The cover member 5 is cylindrical and has an axial through bore in whichthe bit body 2 is inserted. The cover member 5 has an inside diameterwhich is slightly smaller than the diameter of the front portion 2 b ofthe bit body 2 shaped like a circular column, so that the cover member 5attached to the bit body 2 can move back and forth by a specificdistance along the axis of the bit body 2.

The cover member 5 has a magnetic attracting portion 19 formed at oneaxial end thereof (or its front end). The magnetic attracting portion 19has an annular magnet 20 as in the first to third embodiments of theinvention.

The cover member 5 has a circumferential groove 23 formed in its innersurface along its circumference and an elastic annular member 24 fittedin the circumferential groove 23 as in the first embodiment. The elasticannular member 24 projects inwardly from the inner surface of thecylindrical cover member 5.

The circular column-shaped front portion 2 b of the bit body 2 has acircumferential groove 13 formed in its outer surface along itscircumference. The circumferential groove 13 has a rear wall surface 15formed on the rear side of a circular column-shaped straight portion 14as a tapered surface reduced in diameter as viewed toward the front endof the bit body 2 and a front wall surface 16 formed on the front sideof the straight portion as a tapered surface enlarged in diameter asviewed toward the front end of the bit body.

The circumferential groove 13 has a width between its front and rearedges (or a length therebetween) which is longer than the axial lengthof the elastic annular member 24 (i.e. the diameter of its crosssection) as in the first embodiment, so that when the cover member 5 isattached to the bit body 2, the elastic annular member 24 can move backand forth between the rear and front wall surfaces 15 and 16 of thecircumferential groove 13.

When the cover member 5 is attached to the front portion 2 b of the bitbody 2, the elastic annular member 24 on the inner side of the covermember 5 is positioned between the front and rear wall surfaces 16 and15 of the circumferential groove 13 of the bit body 2. The elasticannular member 24 and the circumferential groove 13 of the bit body 2serve as movement permitting means for permitting the back and forthmovement of the cover member 5 and retaining means for the cover member5, as described in connection with the first embodiment of theinvention.

When the bit holder device 1 does not hold any screw 3, the magneticforce exerted on the bit body 2 by the magnetic attracting portion 19keeps the cover member 5 retracted relative to the bit body 2, as shownin FIG. 11. In this position, the cover member 5 is positioned by itsrear end 5 a abutting the boundary surface between the rear and frontportions 2 a and 2 b of the bit body 2, i.e. the front end surface 43 ofits hexagonal column-shaped portion. This enables the cover member 5 tostand by in the same position at any time when the bit holder device 1does not hold any screw 3.

When the bit body 2 is inserted in the groove of a screw 3, the magneticforce exerted on the screw 3 by the magnetic attracting portion 19causes the cover member 5 to advance and causes the magnetic attractingportion 19 to hold the screw 3, as shown in FIG. 12.

For changing the bit body 2, the cover member 5 is initially detachedfrom the bit body 2, and then, the bit body 2 is detached from theholder body 4 and changed. In order to detach the cover member 5 fromthe bit body 2, since a force enabling the elastic annular member 24 toundergo elastic deformation and move over the front wall of thecircumferential groove 13 suffices for pulling the cover member 5, it ispossible to detach the cover member 5 from the bit body 2 easily with asingle hand and it is also easy to attach the cover member 5 to the bitbody 2.

Accordingly, it is advantageously possible to change the bit body 2easily and quickly, since the cover member 5 is easy to attach anddetach for changing the bit body 2.

It is also be possible to form the circumferential groove 13 in eitherthe bit body 2 or the cover member 5 and provide the elastic annularmember 24 on the other, as in the first embodiment.

Further, the rear portion of the bit body 2 may be formed integrallywith the shank 6 so that the bit body 2 is directly attached to anelectric rotating tool B without employing any holder body 4. Even insuch a case, the elastic annular member 24 and the circumferentialgroove 13 facilitate the attachment and detachment of the cylindricalcover member 5 to and from the bit body 2.

FIGS. 13 and 14 show a fifth embodiment of this invention.

According to the fifth embodiment, an elastic annular member 24 providedon the inner side of a cover member 5 and an elastic annular member 24provided between the front portion 2 b of a bit body 2 and the inside ofthe cover member 5 restrict the back and forth movement of the covermember 5.

When the cover member 5 does not hold any screw, the cover member 5stays retracted relative to the bit body 2 and is positioned by theelastic annular member 24 abutting the rear wall surface 15 of thecircumferential groove 13 of the front portion 2 b of the bit body 2 soas not to move back to any further extent. Thus, the elastic annularmember 24 serves not only as retaining means as described in connectionwith the fourth embodiment of the invention, but also as positioningmeans for determining the standby position of the cover member 5 whenthe bit holder device 1 does not hold any screw 3. Other construction ofthis embodiment is equal to that of the fourth embodiment, and commonsymbols with the fourth embodiment are used to denote common parts.

The fifth embodiment of this invention also facilitates the detachmentof the cover member 5 from the bit body 2 or its attachment and therebyany job of changing the bit body 2.

The bit body 2 may be formed integrally with the shank 6 so that the bitbody 2 is directly attached to an electric rotating tool B withoutemploying any holder body 4. Even in such a case, the elastic annularmember 24 and the circumferential groove 13 facilitate the attachmentand detachment of the cylindrical cover member 5 to and from the bitbody 2.

It should be noted that this invention is not limited to any of theembodiments as described above.

Although the cover member 5 is provided with the elastic annular member24, while the circumferential groove 13 is formed in the holder body 4,according to the first, second or third embodiment, it is alternativelypossible to provide the holder body 4 with an elastic annular member 24and form in the cover member 5 a circumferential groove 13 in which theelastic annular member is engageable.

Referring likewise to the fourth or fifth embodiment, it is possible toform the circumferential groove 13 in one of the front portion 2 b ofthe bit body 2 and the cover member 5 and provide the other with theelastic annular member 24.

The position of the magnet 20 is not limited to the front end of thecover member 5. It is also possible to form the cover member 5 from amagnetic material and attach a magnet 20 to the sidewall of the trunkportion of the cover member 5 so that the magnet 20 may magnetize thefront end of the cover member 5 to form a magnetic attracting portion 19for holding screw 3.

Referring to the holding means 9 for holding the bit body 2, it isuseful that the groove 10 formed in the inner wall of the first holdingport 7 for fitting the stopper ring 11 therein have a distance betweenits front and rear edges which is slightly greater than the distancebetween the front and rear edges of the stopper ring 11. This provides aplay to the bit body 2 when the bit body 2 is held in the first holdingport 7. Accordingly, it is advantageously possible to allow the bit body2 to retract from the groove on the head of a screw 3 so as to releasethe engagement therebetween without causing a damage to the groove in acase, for example, that an excessive load bears between the screw 3 andthe bit body 2 when the screw 3 is completely driven into the workpieceA.

INDUSTRIAL APPLICABILITY

This invention is applicable to any product for holding a screw againstdisengagement from a bit body inserted in the groove on the head of thescrew.

1. A bit holder device for driving a screw, while holding the screw against detachment from a bit body with retaining a state where an end of the bit body is inserted in a groove on a head of the screw, the device comprising: a cylindrical cover member removably fitted about the bit body from the end of the bit body, the cover member having an end including a magnetic attracting portion for magnetically attracting the head of the screw, the bit body protruding from the end of the cover member.
 2. A bit holder device as set forth in claim 1, wherein the bit body is removably held by a holder body having a shank in its rear portion, and the cover member is fitted about the holder body.
 3. A bit holder device as set forth in claim 2, wherein movement permitting means is provided between an inner surface of the cylindrical cover member and an outer surface of the holder body for permitting an axial back and forth movement of the cover member relative to the holder body.
 4. A bit holder device as set forth in claim 3, wherein the movement permitting means comprises a circumferential groove formed in an outer surface of the cylindrical holder body; and an elastic annular member provided on an inner surface of the cover member to be engaged with the circumferential groove, the circumferential groove having an axial length which is greater than that of the elastic annular member.
 5. A bit holder device as set forth in claim 4, wherein the holder body is formed in a cylindrical shape comprising a portion forward of the circumferential groove having a diameter which is equal to, or slightly smaller than an inside diameter of the elastic annular member.
 6. A bit holder device as set forth in claim 5, wherein the magnetic attracting portion comprises an annular magnet provided at a front end of the cover member, and the bit body has a tapered end portion situated across a front end surface of the magnet.
 7. A bit holder device as set forth in claim 1, wherein the bit body has a shank integrally formed with its rear portion, and the cover member is directly fitted about the bit body.
 8. A bit holder device as set forth in claim 4, wherein the holder body has a raised portion formed at its rear end for positioning the cover member fitted about the holder body.
 9. A bit holder device as set forth in claim 1, wherein the cover member is held by retaining means for preventing detachment from the bit body, the retaining means being formed of an elastic material to allow the attachment and detachment of the cover member by a human force.
 10. A bit holder device as set forth in claim 9, wherein the bit body is removably held by a holder body having a shank in its rear portion; the cover member is removably fitted about the holder body; and movement permitting means is provided between an inner surface of the cylindrical cover member and an outer surface of a holder body for permitting an axial back and forth movement of the cover member relative to the holder body, the movement permitting means comprising a circumferential groove formed in the outer surface of the cylindrical holder body, and an elastic annular member provided on the inner surface of the cover member to be engaged with the circumferential groove, the circumferential groove having an axial length which is greater than that of the elastic annular member, the elastic annular member serving as the retaining means.
 11. A bit holder device as set forth in claim 9, wherein the bit body has a shank integrally formed with its rear portion; the cover member is directly fitted about the bit body; and movement permitting means is provided between an inner surface of the cylindrical cover member and an outer surface of the bit body for permitting an axial back and forth movement of the cover member relative to the bit body, the movement permitting means comprising a circumferential groove formed in the outer surface of the bit body, and an elastic annular member provided on the inner surface of the cover member to be engaged with the circumferential groove, the circumferential groove having an axial length which is greater than that of the elastic annular member, the elastic annular member serving as the retaining means. 